1. Field of the Invention
The present invention relates to liquid/vapor absorption refrigeration systems, and particularly to a hybrid aqua-ammonia and lithium bromide-water absorption chiller.
2. Description of the Related Art
Liquid/vapor absorption systems using ammonia refrigerant, often referred to as aqua-ammonia systems, typically utilize absorber heat exchange or generator/absorber heat exchange (GAX) cycles carried out in absorption refrigeration chillers for cooling, typically in the form of a chilled water supply directed to a hydronic loop cooperating with an indoor coil and other heat exchange components for transferring the cooling effect to a space to be conditioned. The basic components of such a chiller apparatus include an absorber, generator, condenser and evaporator, along with the necessary piping for the ammonia refrigerant and the water-based absorption fluid. Heat for the generator is typically supplied by a burner, and a circulating pump is required for directing the absorption fluid through the apparatus components.
The generator of a typical aqua-ammonia absorption system operates as a distillation column and typically includes a boiler, a stripping section or stripper, and a rectifying section. The composition feed to the generator is an ammonia-rich liquor from the system absorber, which is introduced to the generator at one or more feed or inlet points. The boiler is designed to produce liquid and vapor counter-flow coincident with heat input. Prime heat is introduced over a finite length or height of the boiler, resulting in a significant change in ammonia concentration in the area of heat input.
The stripping section includes all sections of the generator column that are below the highest (i.e., coldest) feed point. In the stripping section, heat is recovered from solution, leaving the bottom of the distillation column, the recovered heat being returned to the portion of the column above the boiler. The stripping section includes three portions, including a solution-heated-desorber (SHD), either an adiabatic desorber or a generator-absorber heat exchange (GAX) desorber, and the boiler. The SHD is the portion of the stripping section that extracts heat from weak solution, i.e., the solution from the bottom of the generator column, before the weak solution is routed to the absorber. The adiabatic desorber of the stripping section has no heat input and is typically located between the coldest feed point and the SHD. The GAX desorber receives heat from the absorber, either by heat transfer using weak liquor from the bottom of the generator column or from a secondary fluid. Typically, a generator in a GAX aqua-ammonia absorption system will have a GAX desorber or an adiabatic desorber, but not both. When the system utilizes strong liquor GAX, an adiabatic section is used, whereas a GAX desorber is used for weak liquor GAX or secondary fluid GAX.
The feed to the generator column from the system absorber is a rich liquor, which is a solution having a comparatively high ammonia content. Such rich liquor typically has 40% to 50% ammonia, but under some operating conditions, the ammonia content may be as low as about 20%. Such a rich liquor is contrasted to a weak liquor directed from the generator to the absorber, which is a water-rich composition having between about 1% and about 15% ammonia at rating conditions, and typically between about 3% and about 5% ammonia. In conventional strong-liquor GAX absorption cycles, heat is recovered by passing a portion of the strong liquor through a heat exchanger in the GAX absorber, and heating the solution above its bubble point so that it becomes a two-phase mixture. The portion of the strong liquor not passed through the GAX heat exchanger is introduced into the generator at or near the bottom of the rectifier as a single-phase liquid at or below the bubble point temperature. The second feed stream to the generator is that portion of the strong liquor that is passed through the GAX absorber. The second feed stream, comprising liquid and vapor, is introduced into the generator at a lower location than the first single-phase liquid feed. Thus, conventional strong liquor GAX is not separated into liquid and vapor components, but is introduced into the generator together at a common point.
Aqua-ammonia absorption chillers are limited in their applications due to relatively high generator temperatures and high operating pressures when used to produce evaporator temperatures below 0° C. It would be desirable to adapt the versatility and relative simplicity of the aqua-ammonia absorption chiller to applications where temperatures below 0° C. could be achieved, preferably with lower operating pressures and generator temperatures.
Thus, a hybrid aqua-ammonia and lithium bromide-water absorption chiller solving the aforementioned problems is desired.